It is now common to fit filter devices to central heating systems, to remove magnetic and non-magnetic particles from the system water as it circulates around the system. Such filters are useful in all types of central heating system, from small domestic systems with a single circuit and a few radiators, to the largest systems in factories and other industrial sites.
At present, filters are available for domestic systems, which typically use 22 mm or 28 mm copper pipe for the main heating circuit(s). These filters typically have a body made from plastics, for example, glass-reinforced nylon. Various features are known which provide for easy and compact installation in a domestic setting. For example, the Applicant's co-pending application published as GB2502383 discloses an in-line fitment for a filter which includes two sockets, one socket having a greater pipe receiving depth than the other socket. Where some manipulation of the pipework is possible, this provides for easy attachment of the fitment to the heating circuit, where the parts of the fitment which attach to the filter are guaranteed to be at exactly the correct spacing for attachment of the filter.
Filters are also available for larger systems, which use 2 inch (around 50 mm) or greater diameter pipe for the heating circuit(s). For example, the filters sold under the trade mark “Magnaclean® Commercial” fit into this category. These filters are essentially in the form of a large, heavy, cast container, with an inlet and an outlet on either side, a removable lid, and magnets extending into the container to attract and retain magnetic particles from system water as it flows through the filter. These large filters are typically connected into the heating circuit by providing a welded flange on the inlet and outlet of the filter. A similar flange can be welded onto the pipe ends to be connected, and each pipe flange is then bolted to its corresponding filter flange, some sealing material having been placed in between.
However, there is a class of medium-sized central heating systems for which neither of these types of filters are particularly well suited. These systems typically use steel pipe, between 35 mm and 42 mm in diameter. The pipes are usually joined either by tapered threads, which are typically made as required using a die, or by crimping, for example using the “XPRESS”® crimping system. These pipes are inflexible, which makes it impossible to use the in-line fitment as described in GB2502383. Also, the size of the tools used, and the forces typically applied to pipework during installation of these systems, makes damage to a plastic-bodied filter likely. However, large filters such as the Magnaclean® Commercial are expensive to manufacture, and rather over-specified in terms of the system pressure and flow rate which is typical in medium-sized (35-42 mm) systems.
It is an object of this invention to provide a magnetic filter which is suitable for use in these medium-sized central heating systems.